


The Imposter

by Starchart



Category: Harry Potter - J. K. Rowling
Genre: Alternate Universe - Canon Divergence, Background Relationships, Crack Treated Seriously, Family Bonding, Fluff and Humor, For Want of a Nail, Gen, M/M
Language: English
Status: In-Progress
Published: 2019-02-26
Updated: 2019-07-05
Packaged: 2019-11-06 05:20:55
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 3,727
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17933612
Author URL: https://archiveofourown.org/users/Starchart/pseuds/Starchart
Summary: In this universe, Sirius Black doesn't leave England after Harry's third year, he goes to visit Alastor Moody. In this universe, Barty Crouch can't get the drop on Moody. In this universe, it isn'tCrouchwho's drinking polyjuice.Hogwarts, meet Professor Alastor Moody who is definitely not Sirius Black.Oh, and yeah, Moody and Lupin got together. Who knew?





	1. Introduction

**Author's Note:**

  * For [Spirolateral](https://archiveofourown.org/users/Spirolateral/gifts).



In most universes, Sirius Black spent the summer before Harry Potter's fourth year of school wandering the world. In this one, he went to visit Mad Eye Moody.

Now, it wasn't probably the _safest_ thing to do. Moody had a right eye (or maybe left eye?) for a curse and was rather trigger happy, to say the least. But Sirius had never had too great a head for threats. And he managed to shout out loud that Peter Pettegrew had been the secret keeper, which brought the fight to a temporary truce as Moody's distrust of authority warred with his distrust of the man not currently cursing him at the moment.

And after, when Moody had pumped him full of veritaserum from his private store he was sure hadn't been tampered with—who would have known that Moody kept most of what he considered important in the magically expanded wooden leg? Well, other than anyone who'd given it a moment of thought and knew his perfection of the art of paranoia—Moody had finally been convinced that Sirius had been falsely accused. And so Sirius had a good hot bath, a warm meal (not too _tasty_ perhaps, as Moody wasn't the _best_ cook and he didn't trust anyone to prepare his meals, but it was better than most of the dog food Sirius had gotten), and a nice place to sleep. Moody even told the dementors off, which was something that Sirius would never have gotten away with doing.

Moody mentioned that he had been hired by Dumbledore to teach DADA next year, but the new information about Peter . . . angered him, to say the least. He hadn't known the Potters very well, but he took betrayals seriously.

So the two men spent a great deal of time trying to figure out how to track down a rat. A single rat, who could be almost anywhere in the world by then.

Well, it was a challenge. Moody didn't even have to stretch things out so that no search took place before Sirius had stopped looking like he was a hop skip and a jump from anemia. And, in spite of the years of Azkaban, Sirius slowly recovered. His health wasn't perfect, but it was much better.

And so Sirius was there the night that Barty Crouch Jr snuck up on Moody. Or tried to. Sirius's shout alerted Moody, and Crouch, who was not expecting to face a very enraged Sirius Black, went down, wand arm gripped securely in Padfoot's none-too-gentle jaws.

The Aurors would be there soon, but Moody had more than enough time to try to drug Crouch with veritaserum. 

The two of them listened to Crouch's plans with shock.

"Why didn't we think of that?" Moody asked.

Sirius shook his head. "What do you mean?"

Moody grinned. "It's a great plan!" 

Sirius looked concerned. "Sir, I don't think getting kidnapped by You-Know-Who generally is a good thing . . ."

Moody barked out a laugh. "No, not that. I mean, you're no fit shape to go chasing all over the world for your traitor. But I am. And your Lupin was the last competent teacher in the past ten years. And much as I'd appreciate the chance to influence the next generation . . . I think you can do well enough. Just stay in character." 

Sirius looked like he'd been hit with a ton of bricks but nodded. 

And then, Moody had Sirius change back into Padfoot, his "guard dog" so that when the Aurors came, they'd only see one escapee of Azkaban. There was a big fuss about "this can't be Crouch" and Fudge seemed to want to suggest that it was all a bad joke and a prank gone wrong and this must be some muggle from the pub who'd broken in because he'd had too much to drink and only the blank stares of every single responding Auror stopped him. They still were arguing about what everything meant as the group left.

Later that night, after everyone was gone, Sirius stared up at the sky. "I'm sorry Prongs . . . your squid was cool, but _this_ will be the best prank in Hogwarts history."


	2. Chapter 2

Sitting on the Hogwarts Express, Harry picked up Sirius's last letter from the thick stack of letters on his lap to read again.

_Prongslet,_

_I'm looking forward to seeing you this September and getting to know you better. Moony is looking over my shoulder and telling me that I should give you a hint, but I already swore him to secrecy before I mentioned that I hadn't let you in on the secret. It will be one of the best pranks ever!_

Harry this is Remus. Don't let Padfoot's cryptic message worry you, everything's fine. Padfoot just enjoys drama and is looking forward to awing you with his brilliance. Don't believe him. It's not all his.

_It is too! Or at least, it'll be all me doing it. And you'll be so excited when you see how. Remus is giving me a look again, but don't worry, it'll be 100% safe._

Remus again. Usually I'd say believe him when he says anything is 100% safe if you want to keep all of your toes, but in this case, it's actually mostly true.

_Moony, you wound me! That accident in fifth year was almost entirely Snivelus's fault. And no I'm not letting you take the quill again. I know I was the one to add the fireworks, Harry doesn't need to hear about that bit._

_But anyway, Harry, I'm sending you another of my old novels. It still has Remus's tea stains on it._

I resent the implication that I usually get tea on my books, Padfoot.

 _Well, yes, but you saw perfectly fit to get them on_ mine.

Yes, I thought you were the traitor, Padfoot, so your books were fair game. And your notes in the margins about how best to take over the ministry didn't exactly inspire confidence in your innocence.

_Yes, but the ministry is a bunch of sheep who couldn't see the nose in front of their eyes if it bit them so I was justified. And almost half of it was from conversations with James._

Hmph.

_Anyway, Prongslet, the chocolate is from Remus again. If it's not enough, we can send more._

Padfoot. It's _chocolate_. You can never have enough.

 _Anyway, we'll see you soon Pronglset,_  
_Padfoot and_ Moony

Harry smiled at the banter. He was pretty sure that they had been playing it up. In the first letters, there had been a small bit of back and forth in the separate letters the two had written and he had mentioned that he found the small conversation fun in his first letter back to them. Afterwards, all of the letters were written together. It made him feel warm that they cared that much.

The chocolate also made him feel warm. The owl had barely been able to fly under the weight of it all.

He hadn't been able to visit Remus over the summer, as there were some fairly harsh laws preventing werewolves from having unsupervised contact with children that Sirius had ranted about at length and visiting Sirius was entirely out of the question as he was supposed to be a fugitive, but the many many letters they had exchanged had never failed to warm him.

He wasn't sure what Sirius was planning, and, to be perfectly honest, was slightly worried. From what he knew, Remus was reasonably safety-conscious, but still.

* * *

Ollivander had looked at Sirius pointedly when Remus Lupin and Alastor Moody had walked into the shop with a nondescript man with an obviously fake French accent and who announced that his name was "Sam White," he had lost his wand and he needed a new one. Remus, as ever, played a good strait man and backed Sirius up without pausing, saying that he'd just met Mr. White at a muggle pub and was showing him around.

James had once remarked that Remus was a good enough strait man that he could convince McGonagall he was strait even if she had just caught Sirius and Remus kissing in a broom closet. Never one to be deterred from taking the bet, especially one revolving around a pun, Sirius and Remus had tested that theory. As it turned out, the verdict was "not quite"—McGonagall had almost seemed to believe that they'd honestly gotten lost looking for their dormitory, never mind that they were fifth years, but the "we weren't kissing" bit had pushed it a bit too far and at "I'm not gay," Sirius had just started laughing, prompting Remus to start laughing too, ruining the whole thing.

In the present, Moody held up well, better than most when exposed to their peculiar brand of insanity. He only had a strangled look on his face. Sirius wondered if he was fighting his Auror instincts to jump on the poor cover story and arrest him our of sheer principle.

Fortunately, Ollivander seemed to take the same stance as the goblins took to Wizarding Laws—if you tell me you're not breaking them, I don't care enough to tell anyone—and Sirius had gotten a new wand.

Afterwards, Moody just told Sirius that he was _never_ letting Sirius choose a cover name ever again.

* * *

As Moody obviously wasn't going to be handing over his magical eye, Sirius had to make a copy. Unfortunately he'd never been a charm master like Moody; Remus (and the traitor, but don't think about him) had been the main one of the Mauraders to figure out the fiddly charms on the Map.

Partly due to the fact that he didn't have a wand for most of the summer, partly due to the fact that once he got a wand, Moody was spending over sixteen hours a day drilling him on the DADA material under the logic that _he_ was not going to be known as an incompetent teacher, and partly due to Sirius's own tendency for procrastination (despite his having assured Moody that he'd gotten the eye thing covered), it was four hours before he had to report to McGonagall to discuss his curriculum that Sirius showed up on Remus's door asking for help.

Remus didn't mind being woken up at 4AM. As this was about the time of the morning that they had not infrequently woken each other up asking for homework help, it almost was like old times. He said that he would find a way to turn Sirius's hair green and silver if Sirius made a habit out of it though.

Even though Remus was reasonably good at charms, four hours was only four hours. He had had to settle for making it roll around randomly in Sirius's eye socket. This caused a bit of an issue given that Sirius had made sure he'd be able to see out of it first. Remus apologized profusely and tried to pat Sirius's back comfortingly as Sirius retched from motion sickness five minutes after he tried it on. After that, Sirius nixed the vision and just decided to rely on a super-sensory charm.

* * *

He didn't think he could be more stunned at realizing that he was going to Hogwarts and _he didn't have a curfew_ but his meeting with McGonagall proved him wrong.

Sirius gaped. "We get _time turners_?" Incredulity was not a look that fit well on Moody's face, but Sirius couldn't help it.

McGonagall just looked over her glasses at him. "Of course we do, Alastor. How else could we teach all of the sections of classes for all years?"

Sirius barely managed to keep track of the rest of the meeting. A _Time Turner_. What havoc would he wreak with this?

* * *

For the next week, the only answer was a lot more cuddling with Moony.

* * *

Sirius had spent a lot of time practicing walking around as Moody. He gradually found that he could get away with the most outrageous things by simply shouting "Constant Vigilance" after. Nothing exactly illegal, but sniffing random things? poking doorframes? shooting stunners into apparently empty space? instructing children to get their parents to enchant their toys to attack random strangers? Apparently, none of these broke suspension of disbelief or hinted to anyone he might not be Alastor Moody.

Moody seemed frustrated by this but encouraged it. "Absurd caricature seems to be the only type of deception you can pull off, and you'd better play to your strengths."

Sirius chose to take this as a complement.

(And Sirius could have sworn he'd heard Moody muttering that enchantments on toys should be standard, so he figured his performance wasn't _too_ over the top.)

This, combined with his innate preference for drama, was why he chose to introduce himself by coming in late, yelling "CONSTANT VIGILANCE" at the top of his lungs as he set off twenty fireworks hidden around the great hall.

He stalked to the staff table. And, looking at the stunned and fearful faces of the students looking up at him, Sirius's only thought was "Yeah, this went well."

**Notes for the Chapter:**

> I've heard people talking about the staffing problem at Hogwarts. This is my totally insane answer, though it would make Hermione's situation third year that much more understandable.


	3. Lesson Plans or Lack Thereof

**Notes for the Chapter:**

> Thank you everyone who's read this!

 

Sirius clunked across the front of the great hall, single-mindedly focused on the chair that he was going to. The magical eye spun wildly in his head. He would normally need to check for traps--he still hadn't _quite_ managed to get it working so that he didn't throw up the moment he looked out of it--but if seven years at Hogwarts had taught him anything, it was how to bluff. Okay, he liked to think that he had been decent at bluffing when he arrived, and the fact that he had spent any time _not_ in detention his first year supported that hypothesis, but his practically daily visits to McGonnegal's office had definitely allowed him to hone his skills.

The staff did admirable jobs of keeping serious, unperturbed faces, though Sirius had more experience than most and could tell what they were thinking. Snape seemed to be plotting murder, as usual. McGonnegal's face was so much like the face she had made when the Mauraders had pulled off their senior prank that Sirius had to stifle a grin. Dumbledore alone was inscrutable. His eyes were twinkling, but they seemed to do that all the time, so the only think he could tell was that he wasn't furious. Oh, well, that's all that was needed.

It was fun to be Mad(-Eye).

The Hogwarts feast was excellent. Particularly because of its lack of any rodent meat. Sirius liked eating rat, partly for the sense of almost-vengeance it gave, but he couldn't deny that his diet had gotten rather monotonous the last time he had been at Hogwarts and rat was the main culprit.

* * *

All in all, it was almost perfect. The only trouble, Sirius realized the next morning, is that students and professors didn't exactly mingle. He had let Harry go back to his dormitory the night before because even he had had the sense that pulling Harry away in the middle of a feast and hugging him as hard as possible would provide a spectacle that would bring awkward questions.

And even though he was going to be doing more mingling than most--after all, he _had_ gotten the headmaster's permission to run harmless out-of-class tactical awareness and strategic planning training exercises for the students in lieu of essays--he could still not find a good time to talk to Harry. On that subject, Sirius vaguely wondered if the Headmaster had realized that he had given Sirius free rein to prank the school in an official capacity. However, he equally well realized that it would have to remain a riddle for the ages as even if Sirius's impassioned monologue about the importance of CONSTANT VIGILANCE had disguised it _once,_ twice was definitely out of the question and Dumbledore would never actually give him a straight answer anyway.

Sirius was arranging his classes as Remus had, as a series of practical demonstrations. Only, unlike Remus's classes, which had focused mostly on magical creatures, Sirius's, as Moody, would be mostly enchanted traps. (Remus had always made sure to be the expert on magical creatures, partially because he found them fascinating and partially, knowing Gryffindors' general standard attitudes towards reading books, so everyone would come to him for questions on the subject and no one would actually look up werewolves. That had worked, better than James had liked to admit.) That style of teaching also had the benefit that Sirius did not need to actually know how to order the standard defense spells in any meaningful order. The Defense teachers had been rubbish in his schooldays and while he knew a great deal about defense, he had picked most of the spells he knew fighting death eaters in the order, figuring out how to _uncurse_ something that his relatives had cursed, or general sneaking into the restricted section, none of which exactly followed a meaningful teaching plan. And, while Auror training _did_ follow such a plan, Moody was known for improvisation. So it was at least mostly in character.

Indeed, the first week went swimmingly, at least from a teaching perspective.

There were ... mixed reactions to the homework. The students loved it. Snape hated it. Win-win as far as Sirius was concerned. 

It also required Remus to come help him with charms. And regardless of the response, any plan which required him to sneak around and hide in broom cupboards with a disillusioned Remus Lupin was a very good plan in his mind.

The Ravenclaws seemed mostly to be using it as an opportunity for research. Even Hermione seemed to be finding it exciting, despite her initial worries. She, along with many of the other more theory-minded students, had come up after class the first day that Sirius had explained his homework policy. His suggestions that this would free up time to focus on other subjects and that he would be focusing at least in part on relatively unknown spells where reading and research would come in handy had turned the students' fears to excitement. It helped, in Hermione's case, that he had used a spell whose discussion had been found in _Hogwarts a History._

It was a reasonable compromise, in Sirius's mind. He would allow students who couldn't figure out how to dispel the prank to come to him for help. He'd give them a few pointers, and if they still couldn't figure it out, he'd remove it and they'd have to write an essay on whatever spell it had been. Either they could accept the slight grade penalty of he'd cast it on them later in the year and give them a second chance. Intercepting him before he'd cast the spell counted for extra credit. The students seemed to particularly like that part, although Luna Lovegood had been the only student to catch him in the act so far.

* * *

It cannot be said that Sirius had a normal relation with his professors when he had been a student. And so what he did next was entirely to be expected. Harry and Hermione and Ron were coming back in from visiting Hagrid. No one else was in the entrance hall.

"Detention, Potter"

Harry, bless his heart, was incensed. He scowled and glared but wasn't going to protest. Hermione, however, had much more of an intact sense of justice in the world. 

"What on earth for, Professor?"

It was just like Crookshanks had said, Sirius thought with some surprise. Crookshanks liked his human, and Sirius at first had thought the cat had been over-exaggerating his human's tendency for protectiveness.

Sirius shrugged. In Mad-Eye Moody's body, it was a strange gesture. "Breathing." Truthfully he hadn't actually thought that far. It had always been James who'd wanted a plan. Sirius had always thought that planning anything specific was just asking for bad luck.

Sirius realized with a small jolt that this wasn't the first time he'd thought of James without overwhelming grief, and that he'd been doing it more and more often lately. It was strange. Remus would probably call it progress. But he was pulled away from his musings back into present.

"You can't be serious," the redhead on Harry's right said, starting to get worked up into a temper.

Sirius paused for a moment to try to fight a smile. Almost no one accidentally gave him such a perfect setup anymore. "Oh, I assure you, I am entirely _Sirius_." Even disguised, he was _never_ going to throw away the opportunity for that pun. Ron didn't get it right away, but he saw Harry look confused, recognizing that _something_ had just been said and Hermione look like someone had just thrown a glass of water on her head. He knew they'd all figure it out. He turned away, just as Ron's further protests were cut off by Hermione treading pointedly on his foot.

"See, James?" Sirius thought with a most unlike-Moody grin on his face as a furious burst of whispering broke out behind him, "I couldn't have planned _that_."

* * *

Sirius wasn't too worried about alienating his godson with a detention. Most students quite liked Sirius's detentions. Unless someone was doing something malicious, 'getting caught' was all Sirius was ever going to write on a detention slip--a practice which Snape had already loudly complained about. Fortunately, Moody was just as stubborn as Sirius so no one expected that to change anything. The few who were doing something malicious would just get lines to write while sitting in a desk with an enchantment which erased parchment randomly when you weren't looking at it. Sirius was proud of the enchantments. But so far his detentions had ended up being mostly about how to prank people more elegantly and how not to get caught. Moody had reluctantly signed off on that state of affairs, when Sirius said that he wouldn't plausibly be able to promise to do anything else. So his first staff meeting, Sirius had delivered an impassioned rant to the rest of the staff that pranks were good for developing student's spatial awareness, and that they were an integral part of the Hogwarts experience that Moody had pre-approved.

But this detention, Sirius purposefully drank polyjuice precisely fifty four minutes before Harry was due to arrive and set out two cups of cocoa. He was looking forward to getting to know his godson.


End file.
